1. Field of the Invention
The present invention relates to a scanning charged particle microscope, image acquisition method, and electron detection method.
2. Description of Related Art
It is known that a scanning electron microscope (SEM) is one example of scanning charged particle microscope.
In a scanning electron microscope, an electron beam derived from an electron gun is sharply focused by an objective lens, deflected by a deflection coil, and enters a sample. The electron beam entering the sample scatters within the sample, resulting in emission of electrons from the sample. The emitted electrons are different in energy, emission angle, and amount of emission, depending on the composition and morphology of the sample. Therefore, a scanned electron image reflecting composition and morphology of the sample is obtained by detecting released electrons by an electron detector while scanning the electron beam.
In such scanning electron microscopy, E-T (Everhart-Thornley) detectors and semiconductor detectors are known as electron detectors for detecting electrons.
An E-T detector has a scintillator to which a high voltage is applied. Electrons released from a sample are drawn by the potential and accelerated. Thus, the electrons enter the scintillator, producing light. The light is converted into electrons, multiplied by a photomultiplier, and detected as an electrical signal.
In a semiconductor detector, electrons released from a sample are directly entered into a PN junction semiconductor. This produces carriers across the PN junction. The carriers are detected as an electrical signal.
JP-A-2005-4995 discloses a detector capable of detecting an energy distribution of signal electrons such as backscattered electrons or secondary electrons. Scanning electron microscopy has the problem that, if the same sample is observed, individual different SEM instruments produce different scanned electron images. One cause of this is that the position at which a semiconductor detector is installed is different for each different instrument and the detected electron energy or emission angle is different for different instruments. Therefore, there is a demand for a scanning charged particle microscope capable of performing imaging under conditions where operating conditions such as detected electron energy and emission angle have been selected. For example, in the scanning electron microscope of the above-cited JP-A-2005-4995, the energy of electrons released from a sample can be selected but the emission angle of the released electrons cannot be selected.